Current commercial decaffeination of coffee is effected by the removal of caffeine from whole, green coffee beans. The beans are first moistened and then extracted with a solvent which is relatively specific for caffeine. The solvents employed commercially are either a chlorinated hydrocarbon solvent, such as discussed in U.S. Pat. No. 3,671,263 to Patel et al. or a caffeine-deficient water solution of green coffee solubles, such as disclosed in U.S. Pat. No. 2,309,092 to Berry et al. which is herein incorporated by reference.
In the decaffeination process of U.S. Pat. No. 2,309,092 which is commonly referred to as the water extraction system (Note: Sivetz, Coffee Processing Technology, Vol. 2, p. 208, AVI Publishing Co., Inc., 1963) the caffeine laden water extract, resulting from contact between caffeine-containing green coffee and the caffeine-deficient water solution, is directly extracted with a solvent in order to remove caffeine. Typically these solvents are the same chlorinated hydrocarbons which are employed in the direct solvent extraction processes, exemplified by the aforementioned U.S. Pat. No. 3,671,263.
It is also known to produce decaffeinated soluble coffee by first stripping and collecting volatile flavor and aromas from an aqueous extract of roasted coffee and then directly contacting the stripped extract with an organic water-immiscible caffeine solvent such as methylene chloride. The decaffeinated extract can then be combined with the collected volatiles and dried to a soluble powder form. Such a process is described in U.S. Pat. No. 2,933,395 to Adler et al. A process of this type could also be applied to aqueous tea extracts.
The coffee industry is desirous of finding systems for decaffeination which will avoid intimate contact (e.g., as in liquid-liquid extraction) between the aqueous extract to be decaffeinated and an organic solvent. Additionally, it would be desirable if these new decaffeination techniques would reasonably permit the use of non-halogenated solvents which might have a relatively low (i.e., much below that of halogenated hydrocarbons) partition coefficient for caffeine. Such materials as liquid triglycerides (e.g., vegetable oils), fatty acids and fatty alcohols are among these low-capacity caffeine solvents which have a desirably high degree of toxicological safety; however, because of the large amounts of these materials that would be required for their use in conventional extraction decaffeination process, they have not been used commercially.
Decaffeination techniques which avoid the use of a solvent such as the resin technique of U.S. Pat. No. 3,108,876 to Turken et al. and the microbiological technique of U.S. Pat. No. 3,749,584 to Kurtzman et al. are known to the art but have not yet been developed commercially. The use of membrane technology such as in dialysis, ultrafiltration and reverse osmosis has not proven to be successful since presently available membranes are not capable of removing virtually all the caffeine from the aqueous extracts without also removing large amounts of non-caffeine coffee solids. The use of membrane solvent extraction techniques, such as described in U.S. Pat. No. 3,956,112 to Lee et al., would not prove practical for the commercial decaffeination of coffee or tea extracts since the swollen, non-porous membranes used in this process will not permit sufficiently high rates of caffeine diffusion from the extract to the solvent, such that virtually all the caffeine is removed from the extract in a reasonable time period.